Digital Spy sat down with Chastain to discuss her intensive research process for the role, and how she got to grips with her character's inscrutable personality.

"She loses herself to her work, she has no personal life. Through this almost-decade journey, she becomes a nothing," Chastain mused.

"She lives, breathes, eats, sleeps this mission. Over the course of this decade, the more she steps up, the more she loses herself."

Chastain went on to discuss the atmosphere on set, which was frequently chaotic with additions being made to the script at the last minute, and also spoke about the decision not to end the film on a note of jingoistic, pro-America triumph.